Industrial abrasive tools often include abrasive grains of a hard substance affixed to a rigid core. The core can be adapted to be manually or power driven in moving contact with a work piece to grind, cut, polish or otherwise abrade the work piece to a desired shape. The abrasive grains are usually attached to the core by a material sometimes called a bond.
The cutting ability of abrasive tools generally diminishes with continued use. Ultimately, a tool wears so much as to become ineffective for further use and should be replaced with a fresh one. Often the wear causing reduced cutting ability is due to reasons such as excessive dulling and loss of the abrasive grit. The grit can be lost when the bond erodes or fractures through contact with the work piece. In many cases, only the abrasive and bond are affected by wear and the core remains substantially intact.
The need to replace worn out abrasive tools is important in certain aggressive cutting applications such as in construction material and industrial grinding. These applications typically involve grinding materials such as metals, natural stone, granite, concrete, organic composites, and ceramics, and mixtures of them. These difficult-to-cut materials tend to rapidly wear out even the most durable abrasive tools which incorporate superabrasive grits, such as diamond and cubic boron nitride ("CBN"). Additionally, construction grinding abrasive tools are frequently quite large. Abrasive wheels of up to several feet in diameter for cutting concrete and other roadway materials are not uncommon. The cost of replacing such tools can be quite high.
To reduce replacement cost, it is usually possible to recondition the core recovered from a worn out tool. This is generally accomplished by removing any residual bond and grit on the core, repairing structural defects in the core and applying a new cutting surface of abrasive grit and bond. Removal of bond and grit from recovered abrasive tools is sometimes referred to as stripping. Stripping is especially important for recovery of industrial grinding tools because industrial projects largely demand grinding to fine tolerances. Residual bond material should be completely removed from a used core to obtain dimensional precision suitable for industrial grinding. Of course, stripping also is important in construction grinding.
Many techniques such as scouring and heating may be used to strip recovered cores. Abrasive tools which employ a metal bond are usually stripped by a combination of chemical and electrochemical processes. That is, the tool may be immersed in a chemical bath which is selectively corrosive to the composition of the bond. A suitable electrical circuit may be applied in a manner which further strips the bond from the core by reverse electroplating.
While significant for many abrasive tool types, the ability to strip the core is particularly important in the development of bonds for so-called Single Layer Metal Bond ("SLMB") type tools. SLMB tools basically are made by applying the grit and a thin coating of a bonding material to the cutting surface of the core. Finally, a bond between the grit and the core is brazed by heat treating the assembly.
Nickel is a component in traditional bonds that can be readily stripped from the core. However, nickel-containing bond materials usually braze at very high temperature, typically well above 1000.degree. C. causing adverse effects. In this temperature range diamond particles graphitize, and sometimes even the core metal distorts. Alternatively, nickel bonds can be effected by electroplating. This process suffers from the drawback that electroplating baths use large volumes of abrasive grit dispersed in the plating liquid. If the grit is diamond or CBN, the plating bath becomes excessively expensive to maintain. Electroplated bonds also do not perform as well as so-called "active" bonds, discussed below, that is, the bonds are not as strong and grains dislodge from the tool more easily. This poor performance is understood to stem from the lack of chemical interaction between the electroplated bond composition and the abrasive grain material.
Active bond alloys which include chemically active components such as titanium have gained popularity in the field of bonds for SLMB tools. Wesgo, Inc. of Belmont, Calif. offers a bond based on copper-silver eutectic with 4.5 wt % titanium under the Ticusil tradename. Although this product provides an easily stripped bond, it is relatively expensive due to the silver content, and its performance in service is moderate.
U.S. Pat. No. 5,102,621 discloses a ternary brazing alloy consisting essentially of 0.5-10 wt % titanium, 10-50 wt % tin and the balance copper. The brazing alloy is directed to forming a brazed joint between a graphite or carbon body and a metal member, primarily in the electronics industry to braze graphite electrodes to copper conductors. The braze alloy was prepared by blending appropriate amounts of copper, tin and titanium and heating the mixture in a crucible. This reference indicates that the braze alloy wets and forms good bonds to graphite.
A preferred SLMB bond alloy has the composition 70 Cu/21 Sn/9 Ti (wt %). The three metal powders can be blended with a liquid binder to obtain a paste. A bond formed by applying the paste to a metal core, depositing abrasive particles in the paste and brazing the alloy at high temperature is strong but unfortunately, is not readily strippable by chemical and electrochemical methods. Such Cu/Sn/Ti-containing bond compositions are thought to strip poorly because
(a) tin-bearing intermetallic phases within the bond are resistant to corrosion by stripping chemicals, and (b) a Ti/Fe/Cu/Sn intermetallic phase is formed which strongly adheres the bond to the core. Tin and titanium are melting point depressants for the alloy and titanium reacts with carbon which beneficially causes the molten bond to wet diamond grit during brazing. Therefore, simply reducing the amount of tin and titanium in the composition to improve stripping ability is undesirable. PA1 (i) about 50-80 wt % copper; PA1 (ii) about 15-25 wt % tin; PA1 (iii) about 5-15 wt % titanium, and PA1 (iv) about 2-150 parts by weight ("pbw") silver per 100 pbw of the total of (i)-(iii), PA1 wherein the weight percentages are based on the total of (i)-(iii). PA1 (1) blending to a uniform mixture a bond composition consisting essentially of PA1 wherein the weight percentages are based on the total of (i)-(iii); and PA1 (2) placing abrasive grains and the bond composition on a cutting surface of the core; and PA1 (3) heating the bond composition to a brazing temperature of at most about 870.degree. C. in a substantially oxygen-free atmosphere for a duration effective to liquefy a major fraction of the composition. PA1 (a) a predominantly iron core; and PA1 (b) abrasive grit bonded to the core by a brazed bond composition consisting essentially of PA1 wherein the weight percentages are based on the total of (i)-(iii).
Cu/Sn/Ti bonds for brazing have traditionally been made by mixing together powders of the three individual components to obtain a uniformly concentrated blend. This process advantageously gave the manufacturer excellent control over the final bond composition because the amount of each of the components could be adjusted separately. It has been discovered that the bond made by a two step method involving first combining the copper and tin components in a bronze alloy, and secondly mixing a powder of the bronze with an appropriate amount of titanium hydride powder and silver, is highly effective for SLMB bonds and is much more strippable than the traditional Cu/Sn/Ti bonds. It has been discovered that adding silver to the copper, tin and titanium ternary bond described in U.S. Pat. No. 5,832,360 affords a strong abrasive bond having improved strippability.
Accordingly, the present invention provides a strippable bond composition for an abrasive tool having a predominantly iron core consisting essentially of
Still further the present invention provides a method of bonding an abrasive grit to a tool having a predominantly iron core, comprising the steps of.
(i) about 50-80 wt % copper; PA2 (ii) about 15-25 wt % tin; PA2 (iii) about 5-15 wt % titanium; and PA2 (iv) about 2-150 pbw of silver per 100 pbw of the total of (i)-(iii); PA2 (i) about 50-80 wt % copper; PA2 (ii) about 15-25 wt % tin; PA2 (iii) about 5-15 wt % titanium; and PA2 (iv) about 2-150 pbw of silver per 100 pbw of the total of (i)-(iii);
Yet further there is provided a single layer metal bonded tool comprising